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Date:      Wed, 14 Mar 2007 09:41:57 -0400
From:      "Justin T. Gibbs" <gibbs@scsiguy.com>
To:        aic7xxx@freebsd.org
Subject:   Re: Adaptec 2940UW with Fujitsu MAN3184M
Message-ID:  <45F7FBA5.4010404@scsiguy.com>
In-Reply-To: <20070314121250.GB2553@radix50.net>
References:  <20070228204034.GA2379@radix50.net> <45E602B3.2020306@paralan.com>	<20070228233314.GA7348@radix50.net> <45E77B30.2090505@paralan.com>	<20070302220950.GD7331@radix50.net> <45E8C36C.1020407@paralan.com> <20070314121250.GB2553@radix50.net>

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Baurzhan Ismagulov wrote:
> 
> I've done some tests (hdparm -tT, build the Linux kernel with ccache)
> and have seen that my SATA 7.2k ST3320620AS outperforms U160 10k
> MAN3184M by up to 30%, so I decided not to use it for the rootfs yet.

Make sure you run a fair test.  Most SCSI drives are shipped from the
factory with the write cache set to "write-through".  SATA and ATA
drives almost always operate in "write-back" mode.  Your 29160 BIOS
should have an option to set the caching mode on a per-target basis.

If you're system is backed up by a UPS or your FS can handle being
lied to, write-back is fine.  Otherwise it's really not a safe option.

--
Justin



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